A carbide end mill is a type of cutting tool used in industrial milling applications. As the name suggests, it is made out of carbide inserts, and is commonly used in computer numerical controlled (CNC) milling machines. Carbide end mills are especially good for high production milling because they allow faster machining and produce superb finishes on metal parts. They are also characterized by the higher temperature tolerance compared with other high speed steel tools, making them one of the most prevalent cutting tools for drilling slots, routing, profiling, plunge cutting, and general milling applications.
Many have wondered about why carbide end mills of distinct brands seem to perform and cost differently. The answer lies in the four main factors – the grade of the carbide they’re made from, the geometry, the coatings, and premium quality control – all of which decide the performance of a carbide end mill. In this article, we’ll address these factors as to how the performance of carbide end mills varies.
It is very common to see end mill manufacturers refer to the carbide material of an end mill as “solid carbide”, but in reality, the material is by no means a solid metal. For the most part, they are actually “cemented carbide”, which is essentially a matrix composed of tungsten carbide held together by cobalt binder. And a thin coating is usually added to further improve cutting performance.
As you may have guessed, the quality of the carbide is determined by the proportion of tungsten carbide grains versus the binder. High quality carbide has less binder, thus tends to be more expensive than carbide containing more binder. Based on this idea, carbide end mills can be classified into different grades relative to the proportion of tungsten carbide grains. And the grade level of carbide end mills in most cases is directly correlated with the quality of cutting performance.
Geometry is another major determinant of cutting performance with a carbide end mill. To illustrate in a friendly language, we’ll cover only some of the most common instances of helix, namely the lower helix, high helix, and variable helix. To start, note that all of these names are more or less derived from the helix angle of the end mill, which refers to the angle between the edge of the spiral flute and the flat bottom of an end mill. A low helix end mill, for instance, has an angle of 35 degrees or less, whereas a high helix unit has that of above 35 degrees.
High helix end mills are characterized by vertical cutting forces, thereby reducing tool deflection. They allow chips to be evacuated more quickly and have less horsepower requirements. High helix end mills are typically used to cut tougher materials. Low helix end mills, on the other hand, are more commonly used in softer materials and are less likely to chatter. Last but not least, the design of variable helix end mills centers on minimizing chatter, and is often considered the state of the art in the modern end mill market.
Adding quality coating is often the most economical way to enhance the performance of an end mill. The titanium-aluminum-nitride (TiAlN) coated end mill is said to have a surface speed 20% higher than an uncoated carbide end mill, and the margin is subjected to rise. Aside from TiAlN, there are many other coatings to choose from as well.
Machinists often find themselves checking and adjusting the diameter of the cutters to ensure there is a proper offset loaded on the machine. But with premium quality control, you can have the cutters made with tight enough tolerances to match most jobs right from the start.
To discuss further, are premium cutters really worth it? By premium cutters we mean, for instance, the higher-tier grade of end mills with the most sophisticated geometry and coatings. From a performance standpoint, a hobbyist would probably find a premium cutter a bit too over the top. You either may not have a machine powerful enough to handle the end mill, or you simply don’t require a premium tool for your lines of works because you are not trying to leverage it for money. But don’t let this discourage you from getting a modern super cutter if the investment fits your cost structure, again, from a performance perspective.
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